1. Field of the Invention
This invention relates to the preparation of refined and purified vinyl fluoride. More particularly, this invention relates to the preparation of purified gaseous vinyl fluoride which, when subjected to polymerization at a pressure less than 140 kp./cm.sup.2 employing a water soluble azo initiator catalyst at 60.degree.-85.degree. C. provides a polyvinyl fluoride which, when employed as a 40 wt. percent suspension in propylene carbonate has an organosol viscosity of about 20 to 100 cP. More especially, the present invention is directed to the preparation of polyvinyl fluoride polymers which are particularly useful as coating agents especially when employed in a suspension in a latent solvent.
2. Discussion of the Prior Art
Vinyl fluoride polymers have excellent resistance to weathering and chemicals and therefore they are widely used for coating surfaces exposed to corrosion such as iron, aluminum and the like. The coating is best performed by applying to the surface to be protected a suspension of polyvinylfluoride in suitable high-boiling diluent such as propylene carbonate or .gamma.-butyrolactone, with the addition of pigments, fillers, stabilizers etc. if desired, and heating it to temperatures above 200.degree. C., whereupon the polyvinylfluoride particles softened by the liquid flow together and form a non-porous, adherent coating. At the same time the organic liquid evaporates and a coating that is free of solvent is achieved. The high-boiling diluents are also referred to as latent solvents. Latent solvents other than propylene carbonate or .gamma.-butyrolactone may be used, e.g., those listed in DAS No. 1,546,896, page 10.
The economy of this procedure depends to a great extent on the amount of latent solvent that is needed in order to produce a suspension that is sufficiently fluid for the coating. The lower the amount of latent solvent can be kept, the more useful a polyvinylfluoride will be for surface coating. For this purpose, however, it is necessary to prepare polyvinylfluoride with a low organosol viscosity. Hitherto, high pressures of more than 141 kg/cm.sup.2 have been necessary for the production of such vinyl fluoride polymers (cf. DT-OS No. 1,745,748).
It has become desirable to provide a polyvinylfluoride polymer which when employed as a suspension in a latent solvent has a low organosol viscosity. Thus, it has become desirable to provide a refined vinyl fluoride monomer which, when polymerized, provides a polyvinylfluoride polymer which, when in suspension, has a low organosol viscosity. It has thus become desirable to provide a relatively pure vinyl fluoride monomer which can be polymerized to provide a polyvinyl fluoride polymer with the desired physical properties.